Fix UniqueTogetherValidator to handle fields w/ source attr

rest_framework/validators.py

@@ -188,7 +188,8 @@ def __call__(self, attrs, serializer):
                 if attrs[field_name] != getattr(serializer.instance, field_name)
             ]
 
-        condition_kwargs = {source: attrs[source] for source in self.condition_fields}
+        condition_sources = (serializer.fields[field_name].source for field_name in self.condition_fields)
+        condition_kwargs = {source: attrs[source] for source in condition_sources}
         if checked_values and None not in checked_values and qs_exists_with_condition(queryset, self.condition, condition_kwargs):
             field_names = ', '.join(self.fields)
             message = self.message.format(field_names=field_names)

tests/test_validators.py

@@ -683,6 +683,24 @@ def test_nullable_unique_constraint_fields_are_not_required(self):
         result = serializer.save()
         self.assertIsInstance(result, UniqueConstraintNullableModel)
 
+    def test_unique_constraint_source(self):
+        class SourceUniqueConstraintSerializer(serializers.ModelSerializer):
+            raceName = serializers.CharField(source="race_name")
+
+            class Meta:
+                model = UniqueConstraintModel
+                fields = ("raceName", "position", "global_id", "fancy_conditions")
+
+        serializer = SourceUniqueConstraintSerializer(
+            data={
+                "raceName": "example",
+                "position": 5,
+                "global_id": 11,
+                "fancy_conditions": 11,
+            }
+        )
+        assert serializer.is_valid()
+
 
 # Tests for `UniqueForDateValidator`
 # ----------------------------------